1. Field of the Invention
The invention relates to a process for adjusting a motor vehicle part between at least two positions and a drive device for a motor vehicle part which can be adjusted between at least two positions.
2. Description of Related Art
Published German Patent Application DE-OS 29 26 938 discloses a generic process and a generic drive device. Here, in a sliding roof drive, at uniform time intervals, the motor rpm is acquired, the differences of successive values are found, these differences are added to one another when they are larger than a predetermined threshold value, and shut-off or reversal of the motor is triggered as soon as the added sum exceeds a predetermined threshold value.
Published German Patent Application DE 43 21 264 A1 discloses a generic process and a generic drive device. Here, an electric motor drives a motor vehicle window pane. By means of two Hall sensors which are offset by 90 degrees and which interact with a magnet located on the motor shaft, a signal is produced from which the instantaneous period duration of a motor revolution and thus the instantaneous motor rpm are determined at each time at which one such signal enters a control unit for controlling the motor. As soon as the instantaneous rpm change resulting from the difference of two successive rpm measured values exceeds a stipulated threshold value, the motor is reversed in order to release a possibly pinched article.
Published German Patent Application DE 195 11 581 A1 discloses a similar drive device in which, however, the threshold value is variably chosen depending on the position, a memory for certain positions of the adjustment path storing the speed change acquired in an earlier run between two adjacent positions, in order to compute therefrom as a function of position depending on the last currently acquired position and speed the shut-off threshold for the speed.
Published German Patent Application DE 43 12 865 A1 discloses a drive device for a motor vehicle window which acquires the motor rpm by means of two Hall detectors, and which reverses the motor when a threshold is exceeded for the relative change of rpm. In doing so, the threshold value is continually recomputed depending on the acquired motor voltage and the ambient temperature which is determined by a temperature sensor on the motor. In doing so, the status/operating times of the motor are considered in order to be able to draw conclusions about the ambient temperature from the motor temperature.
Published German Patent Application DE 196 18 219 A1 and its corresponding U.S. Pat. No. 6,070,116, disclose determining the rpm threshold or the rpm change threshold of the motor, starting from which reversal of the motor takes place, from the position-dependent rpm data of a reference run which has taken place beforehand depending on the position of the cover for a sliding roof drive. More specifically, to prevent faulty actuation of motor reversal or stoppage, a calculated value is produced from a set of measured values and is compared with two limit values, and only when both limit values are exceeded, is the motor stopped or reversed.
The disadvantage in these generic drive devices which acquire the rpm is that there is not sufficient compensation for vibration influences, for example, when driving over a highly uneven road. Vibrations can lead to serious fluctuations of the rpm, especially also to a periodic fast drop I the motor rpm so that a case of pinching is incorrectly recognized and the motor is turned off or reversed. Thus, there is not always sufficient reliability of the pinching protection.
German Patent DE 42 11 495 C2 discloses pinching protection for blind, awning, louver or swinging door motors, motor torque being monitored for shutting off the motor. The motor is turned off as soon as it has been determined that a limit value for the motor torque has been exceeded a predetermined number of times.
The object of this invention is to devise a drive device for a motor vehicle part which can be moved between at least two positions and a process for adjusting a movable motor vehicle part between at least two positions, by which more reliable acquisition of pinching of an article or body part is obtained.
This object is achieved in accordance with the present invention by a process and by a drive device as described in detail below.
In accordance with the invention, it is advantageous that pinching protection can be optimized in the case of vibration by cutting off overly great changes of rpm.
The upper threshold is preferably chosen to be variable. In this way, the trigger accuracy can be further increased.
The upper threshold is chosen preferably depending on the last determined value of the rpm change or some of the last determined values of the rpm change. This represents an especially feasible embodiment.
In another advantageous embodiment, it is provided that the weight of the value of the force change is zero if the value is below a lower threshold, while the weight for all successive values which exceed this threshold is one. This introduction of a lower limit for consideration of rpm changes or force changes makes it possible to reduce the possibility of faulty triggering due to very slow changes of the action of the force.
Two embodiments of the invention are explained in detail below using the attached drawings.